The present invention relates to an image forming apparatus such as a copying machine and printer, particularly to an image forming apparatus provided with a document reading section permitting automatic reading of a two-sided document, and a method for reading a two-sided document.
In an automatic document reading apparatus, when an image formed on a document is read by the document reading section provided on the image forming apparatus such as a copying machine, a plurality of documents are placed on the document feeding tray. For image formation, each document is automatically picked up and is conveyed to the document reading position. Then the documents having been read are ejected sequentially.
According to the conventional art, when reading the document having a two-sided image, the document on the first face is read at one fixed reading position, and the document is then reversed by the reversing path. After that, the document on the second face is read.
A two-sided document can be read in the following two ways: (a) the first face and second face of a document are read continuously; and (b) the first face of the Nth sheet and the second face of the (N−1)th sheet are read alternately using one reversing path.
When the method (a) is used, the first and second faces of the document are read alternately. This will result in a great loss of time in the reversing section. Reading of the first face is carried out for every other page. This requires much time to perform image formation of the copying machine in the final phase. When the method (b) is used, the first face of the Nth sheet and the second face of the (N−1)th sheet are read alternately, and efficient circulation of the documents is ensured. However, to avoid collision between the trailing edge of the previous page and the leading edge of the following page at the reversing section, the document conveyance intervals must be lengthened, and the document reading time cannot be reduced.
The Patent Document 1 describes a technique wherein a platen is provided as one fixed document reading section and the two-sided document is read according to the aforementioned method (b).
The Patent Document 2 discloses the method (a) wherein a plurality of documents are sequentially fed to one fixed reading position. After the document of the first face has been read, the document is reversed through switching back, and the second face document is then read. A reversing path is provided separately from the normal conveyance path, and the confluence between the reversing path and normal path is located upstream of the reading position, with the result that the method (b) can also be utilized.
[Patent Document 1] Official Gazette of Japanese Patent No. 3122156
[Patent Document 2] Official Gazette of Japanese Patent No. 2758811